Applicant""s hereby claim the right of priority, under 35 U.S.C. xc2xa7 119, based on Japanese Application No. 2000-38602, filed on Feb. 16, 2000, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to a hybrid electric vehicle, and more particularly to a technique for warming up an engine for driving a generator in such a vehicle.
2. Description of Related Art
In recent years, there has been developed a series hybrid vehicle, that is a vehicle equipped with a motor as a source of driving force for the vehicle and a secondary battery, which supplies power to the motor, that is charged by a generator driven by a relatively-small engine. Normally, the series hybrid vehicle operates the engine to run the generator in order to charge the battery if a charging level (SOC: state of charge) of the battery is low.
In general, the series hybrid vehicle, however, does not always charge the battery while the vehicle is running, but charges the battery if the engine is cold after being static for a long period of time. Therefore, if the engine is cold and a large amount of power is required to be generated, the forcible increase in an engine output increases fuel consumption causing a deterioration in fuel economy and also increases oil consumption. This shortens the life of the engine.
To address this problem, Japanese Patent Provisional Publication No. 5-328528 discloses a device, which raises an engine revolution speed to warm up an engine used to drive a generator when the engine is cold.
The rise in the engine revolution speed as disclosed in the above publication, however, results in the increase in noise and vibration. Moreover, if the engine is cold and is not completely smooth, the rise in the engine revolution speed results in the damage on each sliding part of the engine. The increase in the noise and vibration and the damage on each sliding part shorten the life of the engine.
It is therefore an object of the present invention to provide a warm-up control device of a hybrid electric vehicle, which warms up an engine used to drive a generator while extending the life of the engine and improving the quietness.
The above object can be accomplished by providing a hybrid electric vehicle comprising: a generator being rotated by a driving force of an engine to generate power and supply the power to a battery or a motor; a temperature sensing device for sensing a temperature of the engine; and a warm-up control device for controlling a load of the generator and an output of the engine so as to maintain a revolution speed of the engine at a predetermined revolution speed, if the temperature of the engine sensed by the temperature sensing device is not greater than a set temperature.